Technical Field
[0001] The present invention relates to a method for producing a conductive material, a
conductive material obtained by the method, an electronic device containing the conductive
material, a light-emitting device, and a method for producing a light-emitting device.
Background Art
[0002] Conventionally, a method for producing copper wiring by applying a copper foil over
a substrate and etching the same has been used predominantly However, this producing
method, using etching, has a problem that a large amount of liquids and materials
are wasted.
[0003] Then, the following method for producing a wiring board has been known as a method
that does not use etching: a paste-form conductive composition containing metal (e.g.
silver, copper, etc.) particles having a particle diameter of a micron order and an
adhesive (e.g. epoxy-based adhesive, acrylic adhesive, silicone-based adhesive, etc.)
is applied over a substrate, and is heated at 150°C to 180°C (see, for example, Non-Patent
Document 1). By this producing method, distances between metal particles in the conductive
paste are decreased when the adhesive is heated and hardened, and consequently the
metal particles become dense and allow current to pass therethrough, whereby wiring
is produced. With this producing method, however, an electric resistance obtained
is about 5×10
-5Ωcm, which is relatively high for practical application, and therefore, a lower electric
resistance has been demanded.
[0004] Another method has been known also, in which a paste-form conductive composition
obtained by dispersing microparticles of a silver compound such as silver oxide in
a reducing organic solvent is applied over a substrate, and is heated at the vicinity
of 200°C, whereby wiring is produced (see, for example, Patent Document 1). By this
producing method, microparticles of a silver compound such as silver oxide in the
paste change to silver particles when the composition is heated at the vicinity of
200°C, and consequently the silver particles are connected and allow current to pass
therethrough, whereby wiring is produced. However, this producing method has the following
problems: since this method involves a quantitative reduction reaction of the microparticles
of the silver compound such as silver oxide, an intense reaction with the reducing
organic solvent occurs, and owing to a large amount of gas generated, such as a gas
generated by the decomposition of the reducing organic solvent and oxygen gas generated
by the reduction of the silver compound, irregular voids are formed in the conductive
composition, which become stress concentration points that make the conductive composition
easily destroyed and dangerous upon handling. A method modified in such a manner that
silver particles of a micron order are mixed in the composition in order to solve
these problems has been known also, but this merely provides a slight improvement,
though the degree may vary, since the producing method is based on, as the principle,
the metal connection caused by the reduction of microparticles of a silver compound
such as silver oxide.
[0005] Further, a conductive composition containing silver oxide microparticles and a reducing
agent that reduces the same has been known (see, for example, Patent Document 2).
This conductive composition also has a problem in that a high-temperature reaction
heat is generated, which causes a gas to be generated, as in the above-described case.
[0006] A granular silver compound with an organic compound having 1 to 8 carbon atoms being
adhered to surfaces of particles has been known (see, for example, Patent Document
3). When this silver compound is heated, the organic compound on the surfaces act
as a reducing agent, and as a result, the granular silver compound can be reduced
to silver. However, this granular silver compound also has a problem in that a high-temperature
reaction heat is generated, which causes a gas to be generated, as in the above-described
case.
[0007] A conductive paste composed of silver, silver oxide, and an organic compound having
a property of reducing silver oxide has been known (see, for example, Patent Document
4). This conductive paste also has a problem in that a high-temperature reaction heat
is generated, which causes a gas to be generated, as in the above-described case.
[0008] A method for producing a conductive material has been known, in which a porous conductive
material having a voidage of 20 % to 60 % and having a content of an organic substance
of 20 % or less with respect to the mass thereof, which is obtained by heating a composition
composed of silver oxide (I) Ag
2O so as to change the silver oxide into silver, is subjected to plating additionally
(see, for example, Patent Document 5).
[0009] Another method also has been known, in which a paste-form conductive composition
containing a low crystallized silver filler having a particle diameter of a micron
order and silver nanoparticles is applied over a substrate, and is heated at the vicinity
of 200°C, whereby wiring is produced (see, for example, Patent Document 6). By this
producing method, when the foregoing composition is heated at the vicinity of 200°C,
the silver nanoparticles are molten or sintered, and fused so as to adhere to one
another, and allow current to pass therethrough, whereby wiring is produced. In this
producing method, however, there is a problem that the silver nanoparticles cost high.
[0010] In the case of the above-described producing methods, it is necessary to use an adhesive
that makes it difficult to decrease an electric resistance, to use microparticles
of a silver compound as a principal material, such as silver oxide being unstable
and having a strong reducing tendency, or to use a conductive composition containing
expensive silver nanoparticles.
[0011] In the case that such a material of a conventional technique is applied to electronic
components as a bonding material for device electrodes, die attaches, and microbumps,
this material applied, for example, in a light-emitting device is used for mounting
light-emitting elements on a substrate such as a lead frame or a printed circuit board.
Light-emitting elements in recent years have a problem in that an adhesive discolors
owing to heat generated by the application of high current, and an electric resistance
varies with time as an organic component of a resin or the like is degraded by heat
and light. Particularly in the case of the method in which the bonding completely
depends on the adhesion power of the adhesive, it is concerned that there might occur
the following critical problem: when an electronic component is mounted by soldering,
the bonding material may lose an adhesion power under the solder melting temperature,
and separation occurs, which results in failure of lighting.
Patent Document 1: JP 2003-309352 A
Patent Document 2: JP 2004-253251 A
Patent Document 3: JP 2005-200604 A
Patent Document 4: JP 2005-267900 A
Patent Document 5: JP 2006-24808 A
Patent Document 6: 2005-129303 A
Non-Patent Document 1: Yi Li, C.P. Wong, "Recent advances of conductive adhesives as a lead-free alternative
in electronic packaging: Materials, processing, reliability and applications", Materials
Science and Engineering, 2006, R 51, pp.1-35.
Disclosure of Invention
Problem to be Solved by the Invention
[0012] It is an object of the present invention to provide a method for producing a conductive
material that allows a low electric resistance to be generated, and that is obtained
by using an inexpensive and stable conductive material composition containing no adhesive.
Means for Solving Problem
[0013] It has been known conventionally that silver nanoparticles fuse at a low temperature,
but it has not been known that silver particles of a micron order fuse at a low temperature.
The inventors of the present invention found that silver particles of a micron order
fuse when they are heated at a low temperature under oxidizing conditions such as
the presence of an oxide or oxygen, and completed the present invention based on the
foregoing finding.
[0014] The present invention is a method for producing a conductive material, including
the step of sintering a first conductive material composition that contains silver
particles having an average particle diameter (median diameter) of 0.1 µm to 15 µm,
and a metal oxide, so as to obtain a conductive material. Hereinafter, in the present
specification, this producing method is referred to as a first method for producing
a conductive material.
[0015] The present invention is a method for producing a conductive material, including
the step of sintering a second conductive material composition that contains silver
particles having an average particle diameter (median diameter) of 0.1 µm to 15 µm
in an atmosphere of oxygen or ozone, or ambient atmosphere, at a temperature in a
range of 150°C to 320°C, so as to obtain a conductive material. Hereinafter, in the
present specification, this producing method is referred to as a second method for
producing a conductive material.
Effects of the Invention
[0016] The producing methods of the present invention have an advantage in that a conductive
material that allows a low electric resistance to be generated can be produced. Further,
the producing method of the present invention has an advantage in that a conductive
material can be produced with use of an inexpensive and stable conductive material
composition containing no adhesive.
Brief Description of Drawings
[0017]
[FIG. 1] FIG. 1 is an electron micrograph showing a conductive composition obtained
in Example 2.
[FIG. 2] FIG. 2 is an electron micrograph showing a conductive composition obtained
in Reference Example 8.
[FIG. 3] FIG. 3 is a graph showing variation in amounts applied by stamping in Example
34.
Description of the Invention
[0018] The inventors of the present invention found the following. When a composition containing
silver particles having an average particle diameter of 0.1 µm to 15 µm was sintered
in the presence of a metal oxide or in an atmosphere of oxygen or ozone, or ambient
atmosphere, as an oxidizer, the silver particles fused, for example, even at a temperature
in the vicinity of 150°C, whereby a conductive material was obtained. On the other
hand, in nitrogen atmosphere, when a composition containing silver particles having
an average particle diameter of 0.1 µm to 15 µm was sintered, a conductive material
was not obtained at a low temperature in the vicinity of 150°C. Based on this finding,
the inventors of the present invention completed the present invention, i.e., a method
for producing a conductive material which includes the step of sintering a composition
that contains silver particles having an average particle diameter of 0.1 µm to 15
µm, in the presence of a metal oxide, or in an atmosphere of oxygen or ozone, or ambient
atmosphere, as an oxidizer.
[0019] The conventional method for producing a conductive material, which uses microparticles
of a silver compound such as silver oxide and a reducing organic solvent, has a problem
in that a high-temperature reaction heat is generated, whereby gas is generated, as
described above. On the other hand, the method for producing a conductive material
according to the present invention makes it possible to produce a conductive material
without the problem of a gas generated by decomposition caused by heat of abrupt reaction.
[0020] In the method of the present invention for producing a conductive material, the mechanism
of the formation of a conductive material is not clear, but can be presumed as follows.
When a composition containing silver particles having an average particle diameter
of 0.1 µm to 15 µm is sintered in an atmosphere of oxygen or ozone, or ambient atmosphere
as an oxidizer, the silver particles partially are oxidized, and silver oxide thus
formed by the oxidation, at portions in contact with the silver particles, catalytically
exchanges oxygen with the silver particles, so as to repeatedly undergo oxidation-reduction
reactions. Through such a step, the conductive material is formed. When a composition
containing silver particles having an average particle diameter of 0.1 µm to 15 µm
is sintered in the presence of a metal oxide as an oxidizer, the following can be
presumed: the metal oxide already contained in the composition, at portions in contact
with the silver particles, catalytically exchanges oxygen with the silver particles,
so as to repeatedly undergo oxidation-reduction reactions. Through this step, the
conductive material is formed. Since the conductive material is produced by the mechanism
thus presumed, the method of the present invention for producing a conductive material
does not need the use of a conductive material composition containing an adhesive,
and hence, allows a conductive material that generates a low electric resistance to
be obtained using an inexpensive and stable conductive material composition.
[0021] As described above, the present invention is a first method for producing a conductive
material, including the step of sintering a first conductive material composition
that contains silver particles having an average particle diameter (median diameter)
of 0.1 µm to 15 µm, and a metal oxide, so as to obtain a conductive material. With
this first producing method, a conductive material having a low resistance can be
provided. Further, with the first producing method, since silver particles of a micron
order that do not need a special processing can be fused as-is, a conductive material
can be produced easily. Still further, with the first producing method, a conductive
material can be produced using easily-available and inexpensive silver particles.
Still further, the first producing method has an advantage in the following: it is
unnecessary to use an adhesive, microparticles of an unstable silver compound, etc.,
as raw materials. Still further, the first producing method has an advantage in the
following: since only portions at which the silver particles are in contact with one
another are fused by sintering, voids occur, whereby a film-form conductive material
having considerable flexibility can be formed.
[0022] As described above, the present invention is a second method for producing a conductive
material, including the step of sintering a second conductive material composition
that contains silver particles having an average particle diameter (median diameter)
of 0.1 µm to 15 µm in an atmosphere of oxygen or ozone, or ambient atmosphere at a
temperature in a range of 150°C to 320°C, so as to obtain a conductive material. With
this second producing method, a conductive material having a low resistance can be
provided. Further, with the second producing method, since silver particles of a micron
order that do not need a special processing can be fused as-is, a conductive material
can be produced easily. Still further, with the second producing method, a conductive
material can be obtained, with an amount of generated heat being reduced. Still further,
with the second producing method, a conductive material can be produced using easily-available
and inexpensive silver particles. Still further, the second producing method has an
advantage in the following: it is unnecessary to use an adhesive, microparticles of
an unstable silver compound, etc. as raw materials. Still further, the second producing
method has an advantage in the following: since only portions at which the silver
particles are in contact with one another are fused by sintering, voids occur, whereby
a film-form conductive material having considerable flexibility can be formed.
[0023] In the first method for producing a conductive material, the first conductive material
composition preferably further contains either an organic solvent having a boiling
point of 300°C or lower, or water. This is because in the first method for producing
a conductive material according to the present invention, the organic solvent or water
improves the conformability between the silver particles, thereby promoting the reaction
between the silver particles and the metal oxide. In the first method for producing
a conductive material, since the silver particles can be contained in the organic
solvent or water at a high concentration, without the workability being impaired,
the material has smaller shrinkage in volume after sintered. Therefore, it is easy
to estimate dimensions of the conductive material to be obtained. Still further, the
organic solvent preferably contains either a lower alcohol having one or more substituents
selected from the group consisting of lower alkoxy, amino, and halogen, or a lower
alcohol other than the same. Such an organic solvent is preferred since it has high
volatility, and therefore, residues of the organic solvent in the conductive material
obtained after the first conductive material composition is sintered can be reduced.
[0024] In the first method for producing a conductive material, the sintering step preferably
is carried out in an atmosphere of oxygen or ozone, or ambient atmosphere.
[0025] In the first method for producing a conductive material, the sintering step preferably
is carried out at a temperature in a range of 150°C to 320°C.
[0026] In the first method for producing a conductive material, the metal oxide preferably
is one or more selected from the group consisting ofAgO, Ag
2O, and Ag
2O
3.
[0027] In the first method for producing a conductive material, a content of the metal oxide
in the first conductive material composition is 5 percent by weight (wt%) to 40 wt%
with respect to the silver particles.
[0028] In the first method for producing a conductive material, the metal oxide preferably
has an average particle diameter (median diameter) of 0.1 µm to 15 µm.
[0029] Further, the present invention is a conductive material obtained by the first or
second method for producing a conductive material according to the present invention,
wherein the silver particles are fused to one another, and a voidage is 5 percent
by volume (vol%) to 35 vol%. The conductive material has an advantage of a high bonding
strength.
[0030] The conductive material of the present invention preferably has a content of silver
of 70 wt% or more. Further, the conductive material of the present invention preferably
has an electric resistance of 5.0x10
-5Ω·cm or less.
[0031] An electronic device of the present invention is an electronic device containing
the conductive material obtained by the first or second method for producing a conductive
material according to the present invention, wherein the conductive material is used
as a material for electric wiring, component electrodes, die attaches, or microbumps.
[0032] A light-emitting device of the present invention is a light-emitting device containing
the conductive material obtained by the first method for producing a conductive material
according to the present invention, wherein the conductive material is used as a bonding
material for bonding a light-emitting element to a wiring board or a lead frame. Hereinafter,
in the present specification, this light-emitting device is referred to as a first
light-emitting device.
[0033] A light-emitting device of the present invention is a light-emitting device containing
the conductive material obtained by the second method for producing a conductive material
according to the present invention, wherein the conductive material is used as a bonding
material for bonding a light-emitting element to a wiring board or a lead frame. Hereinafter,
in the present specification, this light-emitting device is referred to as a second
light-emitting device.
[0034] A light-emitting device of the present invention is a light-emitting device containing
a conductive material, the conductive material being obtained by heating a conductive
paste containing silver particles having an average particle diameter (median diameter)
of 0.1 µm to 15 µm and alcohol at 150°C to 300°C, wherein the conductive material
is used as a bonding material for bonding a light-emitting element to a wiring board
or a lead frame. Hereinafter, in the present specification, this light-emitting device
is referred to as a third light-emitting device.
[0035] In the third light-emitting device of the present invention, the alcohol preferably
is either a lower alcohol, or a lower alcohol having one or more substituents selected
from the group consisting of lower alkoxy, amino, and halogen.
[0036] In the first, second, and third light-emitting devices of the present invention,
the wiring board preferably includes at least one selected from the group consisting
of a ceramic substrate containing aluminum oxide, aluminum nitride, zirconium oxide,
zirconium nitride, titanium oxide, titanium nitride, or a mixture of any of these;
a metal substrate containing Cu, Fe, Ni, Cr, Al, Ag, Au, Ti, or an alloy of any of
these; a glass epoxy substrate; and a BT resin substrate.
[0037] In the first, second, and third light-emitting devices of the present invention,
the lead frame preferably includes a metal member containing Cu, Fe, Ni, Cr, Al, Ag,
Au, Ti, or an alloy of any of these.
[0038] In the first, second, and third light-emitting devices of the present invention,
the wiring board or the lead frame preferably is covered further with Ag, Au, Pt,
Sn, Cu, Rh, or an alloy of any of these.
[0039] Further, a method for producing the first light-emitting device according to the
present invention includes the steps of applying a first conductive material composition
that contains silver particles having an average particle diameter (median diameter)
of 0.1 µm to 15 µm, and a metal oxide, over the wiring board or the lead frame; placing
the light-emitting element on the first conductive material composition, so as to
obtain a light-emitting device precursor; and sintering the light-emitting device
precursor, so as to obtain a light-emitting device.
[0040] Still further, a method for producing the second light-emitting device according
to the present invention includes the steps of: applying a second conductive material
composition that contains silver particles having an average particle diameter (median
diameter) of 0.1 µm to 15 µm over the wiring board or the lead frame; placing the
light-emitting element on the second conductive material composition, so as to obtain
a light-emitting device precursor; and sintering the light-emitting device precursor
in an atmosphere of oxygen or ozone, or ambient atmosphere, at 150°C to 320°C, so
as to obtain a light-emitting device.
[0041] Still further, a method for producing the third light-emitting device according to
the present invention includes the steps of: applying a conductive paste that contains
silver particles having an average particle diameter (median diameter) of 0.1 µm to
15 µm and alcohol over the wiring board or the lead frame; placing the light-emitting
element on the conductive paste, so as to obtain a light-emitting device precursor;
and sintering the light-emitting device precursor at 150°C to 300°C, so as to obtain
a light-emitting device.
[0042] As the silver particles in the present invention, regarding the type as to the average
particle diameter (median diameter), silver particles of one type may be used, or
alternatively, silver particles of two or more types may be mixed and used. In the
case where the silver particles is of one type, the average particle diameter (median
diameter) is 0.1 µm to 15 µm, preferably 0.1 µm to 10 µm, and more preferably 0.3
µm to 5 µm. In the case where the silver particles of two or more types are mixed,
for example, average particle diameters (median diameters) of the two types are 0.1
µm to 15 µm and 0.1 µm to 15 µm in combination, preferably 0.1 µm to 15 µm and 0.1
µm to 10 µm in combination, and more preferably 0.1 µm to 15 µm and 0.3 µm to 5 µm
in combination. In the case where the silver particles of two or more types are mixed,
the content of the silver particles of the type having an average particle diameter
(median diameter) of 0.1 µm to 15 µm is, for example, 70 wt% or more, preferably 80
wt% or more, and more preferably 90 wt% or more. With this, the electric resistance
can be decreased.
[0043] The average particle diameter (median diameter) of silver particles in the present
invention can be measured by a laser method. It should be noted that the "average
particle diameter (median diameter)" means a value where an accumulated frequency
by volume is 50 %, which is derived from a particle diameter distribution.
[0044] The silver particles in the present invention have a specific surface of 0.5 m
2/g to 3 m
2/g, preferably 0.6 m
2/g to 2.5 m
2/g, and more preferably 0.6 m
2/g to 2 m
2/g. With this, an area where adjacent silver particles are in contact with each other
can be increased. The specific surface of a silver particle as a principal material
of the conductive material composition of the present invention can be measured by
a BET method.
[0045] Though the shape of a silver particle in the present invention is not limited, examples
of the shape include a spherical shape, a flat shape, and a polyhedral shape. The
shapes of the silver particles having an average particle diameter (median diameter)
in a certain range are uniform preferably. In the case where silver particles of two
or more types with different average particle diameters (median diameters) that are
mixed together are used as the silver particles in the present invention, the respective
types regarding the average particle diameters (median diameters) may have the same
shape or different shapes. For example, when silver particles of two types having
an average particle diameter (median diameter) of 3 µm and an average particle diameter
(median diameter) of 0.3 µm are mixed, the silver particles having an average particle
diameter (median diameter) of 0.3 µm may have a spherical shape each, while the silver
particles having an average particle diameter (median diameter) of 3 µm may have a
flat shape each.
[0046] Examples of the metal oxide in the first conductive material composition of the present
invention include silver oxides (e.g. AgO, Ag
2O, andAg
2O
3); chlorites (e.g. potassium chlorite, sodium chlorite, and copper chlorite); chlorates;
chlorates (e.g. potassium chlorate, barium chlorate, calcium chlorate, sodium chlorate,
and ammonium chlorate); perchlorates (e.g. potassium perchlorate, sodium perchlorate,
and ammonium perchlorate); bromates (e.g. potassium bromate, sodium bromate, and magnesium
bromate); iodates (e.g. potassium iodate, sodium iodate, and ammonium iodate); inorganic
peroxides (e.g. potassium peroxide, sodium peroxide, calcium peroxide, magnesium peroxide,
barium peroxide, and lithium peroxide); nitrates (e.g. potassium nitrate, sodium nitrate,
ammonium nitrate, uranyl nitrate, calcium nitrate, silver nitrate, iron (II) nitrate,
iron (III) nitrate, copper (II) nitrate, lead (II) nitrate, and barium nitrate); permanganic
acid; permanganates (e.g. potassium permanganate, ammonium permanganate, sodium permanganate,
zinc permanganate, magnesium permanganate, calcium permanganate, and barium permanganate);
dichromates (e.g. ammonium dichromate, and potassium dichromate); periodates (e.g.
sodium periodate); periodic acid (e.g. metaperiodic acid); chromium oxides (e.g. chromium
trioxide); lead oxides (e.g. lead dioxide); iodine oxides; nitrites (e.g. potassium
nitrite, sodium nitrite, and calcium nitrite); hypochlorites (e.g. calcium hypochlorite);
chlorinated isocyanuric acids (e.g. trichlorinated isocyanuric acid); peroxodisulfates
(e.g. potassium peroxodisulfate, and sodium peroxodisulfate); and peroxoborates (e.g.
potassium peroxoborate, sodium peroxoborate, and ammonium peroxoborate).
[0047] The metal oxide in the first conductive material composition of the present invention
preferably is one or more selected from the group consisting of AgO, Ag
2O, and Ag
2O
3. These metal oxides promote the oxidation reaction of the silver particles, thereby,
as a result, allowing the metal bonding to be achieved at a relatively low temperature.
These metal oxides are preferable since they are decomposed by heat upon sintering,
and thereafter, become silver. In the first conductive material composition of the
present invention, the metal oxide more preferably is AgO. AgO as the metal oxide
has a strong power of oxidation, and an added amount of the metal oxide therefore
can be reduced. As a result, the electric resistance of the obtained conductive material
is decreased, and the mechanical strength of the conductive material is improved.
[0048] As the metal oxide, one type having one average particle diameter (median diameter)
may be used, or a mixture of two types having different average particle diameters
may be used. In the case where the metal oxide is of one type, the metal oxide preferably
has an average particle diameter (median diameter) of 0.1 µm to 15 µm. This is because
in the case where the metal oxide has the above-described average diameter, it is
possible to provide an excellent workability and to enable low-cost production. Further,
in the case where the metal oxide is of one type, the metal oxide preferably has an
average particle diameter (median diameter) of 0.1 µm to 10 µm, and more preferably,
0.3 µm to 5 µm. In the case where the metal oxides of two or more types are mixed,
average particle diameters (median diameters) of the two types are, for example, 0.1
µm to 15 µm and 0.1 µm to 15 µm in combination, preferably 0.1 µm to 15 µm and 0.1
µm to 10 µm in combination, and more preferably 0.1 µm to 15 µm and 0.3 µm to 5 µm
in combination. In the case where two or more of the metal oxides are mixed, the content
of the type having an average particle diameter (median diameter) of 0.1 µm to 15
µm is, for example, 70 wt% or more, preferably 80 wt% or more, and more preferably
90 wt% or more.
[0049] In the present invention, the first conductive material composition preferably further
contains either an organic solvent having a boiling point of 300°C or lower, or water.
This is because in the first method for producing a conductive material according
to the present invention, the organic solvent or water improves the conformability
between the silver particles, thereby promoting the reaction between the silver particles
and the metal oxide. In the present invention, the second conductive material composition
may further contain either an organic solvent having a boiling point of 300°C or lower,
or water. This is because the organic solvent or water improves the conformability
between the silver particles, thereby promoting the reaction between the silver particles
and the metal oxide.
[0050] In the present invention, the organic solvent preferably contains either a lower
alcohol, or a lower alcohol having one or more substituents selected from the group
consisting of lower alkoxy, amino, and halogen. The reason is as follows: such an
organic solvent has high volatility, and therefore, residues of the organic solvent
in the conductive material obtained after the first conductive material composition
is sintered can be reduced. In the second conductive material composition of the present
invention, the organic solvent may contain either a lower alcohol, or a lower alcohol
having one or more substituents selected from the group consisting of lower alkoxy,
amino, and halogen. The reason is as follows: such an organic solvent has high volatility,
and therefore, residues of the organic solvent in the conductive material obtained
after the first conductive material composition is sintered can be reduced. Examples
of the lower alcohol include a lower alcohol having an alkyl group with 1 to 6 carbon
atoms, and 1 to 3, or preferably 1 to 2, hydroxy groups. Examples of the lower alkyl
group include straight-chain or branched-chain alkyl groups such as methyl group,
ethyl group, n-propyl group, i-propyl group, n-butyl group, i-butyl group, sec-butyl
group, t-butyl group, n-pentyl group, i-pentyl group, sec-pentyl group, t-pentyl group,
2-methylbutyl group, n-hexyl group, 1-methylpentyl group, 2-methylpentyl group, 3-methylpentyl
group, 4-methylpentyl group, 1-ethylbutyl group. 2-ethylbutyl group, 1,1-dimetylbutyl
group, 2,2-dimetylbutyl group, 3,3-dimetylbutyl group, and 1-ethyl-1-methylpropyl
group. Examples of a lower alcohol having an alkyl group with 1 to 6 carbon atoms
and 1 to 3 hydroxy groups include methanol, ethanol, ethylene glycol, n-propanol,
i-propanol, triethylene glycol, n-butanol, i-butanol, sec-butanol, t-butanol, n-pentanol,
i-pentanol, sec-pentanol, t-pentanol, 2-methyl butanol, n-hexanol, 1-methyl pentanol,
2-methyl pentanol, 3-methyl pentanol, 4-methyl pentanol, 1-ethyl butanol, 2-ethyl
butanol, 1,1-dimethyl butanol, 2,2-dimethyl butanol, 3,3-dimethyl butanol, and 1-ethyl-1-methyl
propanol.
[0051] In the lower alcohol having one or more substituents selected from the group consisting
of lower alkoxy, amino, and halogen, the substituent is as follows. Examples of the
lower alkoxy include the lower alkyl group having a substitute of-O-. Examples of
the lower alkoxy include methoxy, ethoxy, n-propoxy, i-propoxy, n-butoxy, i-butoxy,
sec-butoxy, t-butoxy, and n-pentyloxy. Examples of the halogen include fluorine, bromine,
chlorine, and iodine.
[0052] Examples of the lower alcohol having not one or more substituents selected from the
group consisting of lower alkoxy, amino, and halogen include methoxymethanol, 2-methoxyethanol,
2-ethoxyethanol, 2-chloroethanol, and ethanolamine.
[0053] The boiling point of the organic solvent preferably is 300°C or lower. More preferably,
the foregoing boiling point is 150°C to 250°C. This makes it possible to suppress
variation in the viscosity of the conductive material composition at room temperature
owing to volatilization of the organic solvent, thereby improving the workability,
and further, it is possible to allow the organic solvent to vaporize completely when
heated.
[0054] Though the added amount of the organic solvent is not limited particularly, since
the necessary viscosity thereof varies with the methods of application of the conductive
material composition. However, in order to reduce the voidage of the conductive material,
the added amount of the same preferably is 30 wt% or less.
[0055] In the present invention, the sintering step may be carried out in non-oxidizing
atmosphere, ambient atmosphere, vacuum atmosphere, oxygen atmosphere, mixture gas
atmosphere, or airflow. In the first method for producing a conductive material according
to the present invention, the sintering step preferably is carried out in atmosphere
of oxygen or ozone, or ambient atmosphere. The reason is as follows: in the case where
the sintering step is carried out in the foregoing atmosphere, the oxidation reaction
is promoted during the sintering step.
[0056] In the present invention, the sintering step preferably is carried out at a temperature
in a range of 150°C to 320°C. The reason is as follows: in the case where the sintering
step is carried out at a temperature in the foregoing range, the metal bonding can
be achieved at a temperature lower than a melting point of a resin package on which
a semiconductor element or the like is mounted. Further, the sintering step preferably
is carried out at a temperature in a range of 160°C to 260°C, or more preferably in
a range of 180°C to 200°C.
[0057] The content of the metal oxide in the first conductive material composition of the
present invention preferably is 5 wt% to 40 wt% with respect to the silver particles.
This is because with the foregoing content, the conductive material obtained has a
greater shear strength. The content of the metal oxide more preferably is 5 wt% to
30 wt%, and further preferably 10 wt%, with respect to the silver particles.
[0058] The conductive material of the present invention may contain particles of a conductive
metal other than silver. Examples of the conductive metal include palladium, platinum,
gold, and copper. Particles of the conductive metal has an average particle diameter
(median diameter) of, for example, 0.1 µm to 15 µm, preferably 0.1 µm to 10 µm, and
more preferably 0.3 µm to 5 µm. Further, the particles of the conductive metal have
a specific area of, for example, 0.5 m
2/g to 3 m
2/g, preferably 0.6 m
2/g to 2.5 m
2/g, and more preferably 0.6 m
2/g to 2 m
2/g.
[0059] Further, the present invention is a conductive material obtained by either the first
or second method for producing a conductive material, in which the silver particles
are fused to one another, and a voidage is 5 vol% to 35 vol%. The conductive material
has an advantage of a high bonding strength. In the conductive material, the voidage
preferably is 5 vol% to 25 vol%, and more preferably 5 vol% to 15 vol%.
[0060] The conductive material of the present invention preferably has a content of silver
of 70 wt% or more. This is because this conductive material has a great bonding strength.
The content of silver more preferably is 85 wt% or more, and further preferably 90
wt% to 100 wt%.
[0061] The conductive material of the present invention preferably has an electric resistance
of 5.0×10
-5Ω·cm or less. This is because this conductive material has a low electric resistance.
The electric resistance more preferably is 1.0×10
-5Q·cm, and further preferably 7.0×10
-6Ω·cm.
[0062] Further, an electronic device of the present invention is an electronic device containing
the conductive material obtained by the first or second producing method of the present
invention, wherein the conductive material is used as a material for electric wiring,
component electrodes, die attaches, or microbumps. The electronic device, obtained
using the foregoing conductive material, has an advantage of a sufficiently small
electric resistance, and less variation in the electric resistance with time. The
electronic device, obtained using the foregoing conductive material, has an advantage
of high reliability, without a possibility of separation of bonded parts owing to
a thermal shock.
[0063] With the present invention, it is possible to obtain a light-emitting device including
a light-emitting element subjected to metal bonding with the foregoing conductive
material as a bonding material. Examples of a method for bonding a light-emitting
element and a wiring board, etc., include, generally, a method using an insulation
adhesive, a method using an organic bonding material such as a conductive adhesive
in which a conductive metal filler is dispersed, and a method using a metal bonding
material such as a high-temperature lead solder or AuSu eutectic. The method using
an organic bonding material, as described above, has a problem in that the organic
component in the material degrades due to light or heat, and as a result causes the
color or the strength to decrease, whereby the lifetime of the light-emitting device
decreases. The method using a metal bonding material has a problem in that a plastic
member of a light-emitting device significantly degrades due to heat since it is exposed
to a high temperature over 300°C upon bonding. In contrast, in the producing method
of the present invention, the conductive material composition contains silver as a
principal component, and does not need an adhesive. Therefore, if the conductive material
obtained by the producing method of the present invention is used as a bonding material,
it hardly is affected by light or heat, and a temperature required upon bonding in
the foregoing producing method is in a range of 150°C to 320°C, which is low. Therefore,
it is possible to prevent a plastic member in a light-emitting device from degrading
due to heat, and hence, the foregoing method is preferable. Further, the method for
producing a conductive material according to the present invention does not cause
a problem of a gas generated by decomposition caused by heat of abrupt reaction. Therefore,
the conductive material obtained, in which the formation of irregular voids is suppressed,
is excellent as a bonding material.
[0064] A light-emitting device of the present invention is a light-emitting device (first
light-emitting device) containing a conductive material obtained by the first method
for producing a conductive material according to the present invention, wherein the
conductive material is used as a bonding material for bonding a light-emitting element
to a wiring board or a lead frame. Using the foregoing conductive material, the first
light-emitting device obtained has an advantage in that it has a sufficiently small
electric resistance, and less variation in the electric resistance with time. Further,
using the foregoing conductive material, the first light-emitting device obtained
has an advantage in that the degradation and discoloration of the wiring board or
the lead frame is suppressed. Still further, the first light-emitting device of the
present invention has advantages in that light output therefrom has less decrease
with time even if the device is driven for a long time, and that the device has long
lifetime.
[0065] A light-emitting device of the present invention is a light-emitting device (second
light-emitting device) containing a conductive material obtained by the second method
for producing a conductive material according to the present invention, wherein the
conductive material is used as a bonding material for bonding a light-emitting element
to a wiring board or a lead frame. Using the foregoing conductive material, the second
light-emitting device obtained has an advantage in that it has a sufficiently small
electric resistance, and less variation in the electric resistance with time. Further,
using the foregoing conductive material, the second light-emitting device obtained
has an advantage in that the degradation and discoloration of the wiring board or
the lead frame is suppressed. Still further, the second light-emitting device of the
present invention has advantages in that light output therefrom has less decrease
with time even if the device is driven for a long time, and that the device has long
lifetime.
[0066] A light-emitting device of the present invention is a light-emitting device (third
light-emitting device) containing a conductive material, the conductive material being
obtained by heating a conductive paste containing silver particles having an average
particle diameter (median diameter) of 0.1 µm to 15 µm and alcohol at 150°C to 300°C,
wherein the conductive material is used as a bonding material for bonding a light-emitting
element to a wiring board or a lead frame. Using the foregoing conductive material,
the third light-emitting device obtained has an advantage in that it has a sufficiently
small electric resistance, and less variation in the electric resistance with time.
Further, using the foregoing conductive material, the third light-emitting device
obtained has an advantage in that the degradation and discoloration of the wiring
board or the lead frame is suppressed. Still further, the third light-emitting device
of the present invention has advantages in that light output therefrom has less decrease
with time even if the device is driven for a long time, and that the device has long
lifetime.
[0067] In the present invention, the wiring board is not limited particularly as long as
a conductive material composition or a conductive paste can be applied over a surface
of the wiring board. Examples of the wiring board include a semiconductor element;
a ceramic substrate containing aluminum oxide, aluminum nitride, zirconium oxide,
zirconium nitride, titanium oxide, titanium nitride, or a mixture of the same; a metal
substrate containing Cu, Fe, Ni, Cr, Al, Ag, Au, Ti, or an alloy of the same; a glass
epoxy substrate; a BT resin substrate; a glass substrate; a resin substrate; and paper.
Using such a wiring substrate, the first, second, or third light-emitting device of
the present invention has excellent heat resistance. Besides, according to the producing
method of the present invention, a temperature for heating may be low. Therefore,
a wiring board vulnerable to heat, such as that made of a thermoplastic resin, can
be used.
[0068] Preferable as the wiring board is a ceramic substrate containing aluminum oxide,
aluminum nitride, zirconium oxide, zirconium nitride, titanium oxide, titanium nitride,
or a mixture of the same. In the case where the wiring substrate is a ceramic substrate,
when a light-emitting element is made of a single crystal having a small coefficient
of linear expansion, it is possible to prevent thermal stress from being applied to
bonded portions at which the substrate and the light-emitting element are bonded.
Further preferable as the wiring board is a ceramic substrate containing aluminum
oxide. This is because in the case where the wiring board is a ceramic substrate containing
aluminum oxide, the costs of the light-emitting device can be reduced.
[0069] In the present invention, used as the lead frame is, for example, a metal frame made
of copper, iron, nickel, chromium, aluminum, silver, gold, titanium, or an alloy of
the same. Among these metals, copper, iron, or an alloy of the same is preferable.
As the lead frame, that made of a copper alloy is preferable in a light-emitting device
that requires heat dissipation, and an iron alloy is preferable in a light-emitting
device that requires reliability of bonding with a semiconductor element.
[0070] In the present invention, a surface of a portion of the wiring board or the lead
frame on which the bonding material is to be applied may be coated with silver, an
oxide of silver, a silver alloy, an oxide of a silver alloy, Pt, a Pt alloy, Sn, a
Sn alloy, gold, a gold alloy, Cu, a Cu alloy, Rh, a Rh alloy, or the like, and preferably
with an oxide of silver (silver oxide). The reason is as follows: since the surface
part of the portion on which the bonding material is to be applied is made principally
of silver, the surface part of the portion on which the bonding material is to be
applied, if coated with silver oxide, have excellent fusibility with the bonding material.
The coating can be carried out by plating, vapor deposition, sputtering, spreading,
or the like.
[0071] In the present invention, a surface of the light-emitting element that is to be fused
with the bonding material may be coated with silver, a silver alloy, Pt, a Pt alloy,
Sn, a Sn alloy, gold, a gold alloy, copper, a copper alloy, Rh, a Rh alloy, or the
like, and preferably is coated with silver. The reason is as follows: since the surface
part of the portion on which the bonding material is to be applied is made principally
of silver, the surface part of the portion on which the bonding material is to be
applied, if coated with silver, have excellent fusibility with the bonding material.
The coating can be carried out by plating, vapor deposition, sputtering, spreading,
or the like.
[0072] In the first, second, and third light-emitting devices of the present invention,
the lead frame preferably includes a metal member containing Cu, Fe, Ni, Co, Cr, Al,
Ag, Au, Ti, or an alloy of the same, and more preferably includes a metal member containing
Cu, Fe, Ni, Co, or an alloy of the same. The wiring board or the lead frame preferably
is coated further with Ag, Au, Pt, Sn, Cu, Rh, or an alloy of the same, and more preferably
with Ag, Au, Pt, or an alloy of the same.
[0073] Further, the present invention is a method for producing the first light-emitting
device according to the present invention, and the method includes the steps of: applying
a first conductive material composition that contains silver particles having an average
particle diameter (median diameter) of 0.1 µm to 15 µm, and a metal oxide, over the
wiring board or the lead frame; placing the light-emitting element on the first conductive
material composition, so as to obtain a light-emitting device precursor; and sintering
the light-emitting device precursor, so as to obtain a light-emitting device. With
the method for producing the first light-emitting device, an organic material in the
board or the lead frame can be prevented from degrading or discoloring, and a light-emitting
device with high quality and high volume production capability can be produced easily.
In the method for producing the first light-emitting device, the first conductive
material composition preferably further contains either an organic solvent having
a boiling point of 300°C or lower, or water. The organic solvent preferably contains
either a lower alcohol, or a lower alcohol having one or more substituents selected
from the group consisting of lower alkoxy, amino, and halogen. The reason is as follows:
if the first conductive material composition further contains the organic solvent
or water, the silver particles can be contained in the organic solvent or water at
a high concentration, without the workability being impaired, and therefore, the material
has smaller shrinkage in volume after sintered. Consequently, it is easy to estimate
dimensions of the conductive material to be obtained. Still further, since the conductive
material obtained has smaller shrinkage in volume, closer adhesion thereof with the
wiring board or the lead frame can be provided.
[0074] Further, the present invention is a method for producing the second light-emitting
device, and the method includes the steps of applying a second conductive material
composition that contains silver particles having an average particle diameter (median
diameter) of 0.1 µm to 15 µm over the wiring board or the lead frame; placing the
light-emitting element on the second conductive material composition, so as to obtain
a light-emitting device precursor; and sintering the light-emitting device precursor
in atmosphere of oxygen or ozone, or ambient atmosphere, at 150°C to 320°C, so as
to obtain a light-emitting device. With the method for producing the second light-emitting
device, an organic material in the board or the lead frame can be prevented from degrading
or discoloring, whereby a light-emitting device with high quality and high volume
production capability can be produced easily. Further, with the method for producing
the second light-emitting device, metals can be bonded at a relatively low temperature
of 150°C to 320°C, and the bonded portion has a re-melting temperature equivalent
to the melting point of silver of 962°C. Therefore, there is an advantage in that
the reliability is not impaired even when the bonded portion is exposed to a temperature
of 250°C to 300°C at which the light-emitting element to be obtained is mounted on
a substrate. In the method for producing the second light-emitting device, the second
conductive material composition may further contain either an organic solvent having
a boiling point of 300°C or lower, or water. The organic solvent may contain either
a lower alcohol, or a lower alcohol having one or more substituents selected from
the group consisting of lower alkoxy, amino, and halogen. In the case where the second
conductive material composition further contains the organic solvent or water, the
silver particles can be contained in the organic solvent or water at a high concentration,
without the workability being impaired, the material has smaller shrinkage in volume
after sintered. Therefore, there is an advantage that it is easy to estimate dimensions
of the conductive material to be obtained. Further, since the shrinkage in volume
of the conductive material obtained is small, there is an advantage that closer adhesion
thereof with the wiring board or the lead frame can be provided.
[0075] Further, the present invention is a method for producing the third light-emitting
device, and the method includes the steps of: applying a conductive paste that contains
silver particles having an average particle diameter (median diameter) of 0.1 µm to
15 µm and alcohol over the wiring board or the lead frame; placing the light-emitting
element on the conductive paste, so as to obtain a light-emitting device precursor;
and sintering the light-emitting device precursor at 150°C to 300°C, so as to obtain
a light-emitting device. With the method for producing the third light-emitting device,
an organic material in the board or the lead frame can be prevented from degrading
or discoloring, and a light-emitting device with high quality and high volume production
capability can be produced easily. Further, with the method for producing the third
light-emitting device, metals can be bonded at a relatively low temperature of 150°C
to 300°C, and the bonded portion has a re-melting temperature equivalent to the melting
point of silver of 962°C. Therefore, there is an advantage in that the reliability
is not impaired even when the bonded portion is exposed to a temperature of 250°C
to 300°C at which the light-emitting element to be obtained is mounted on a substrate.
In the case where the conductive paste further contains alcohol, the silver particles
can be contained in the alcohol at a high concentration, without the workability being
impaired, the material has smaller shrinkage in volume after sintered. Therefore,
there is an advantage that it is easy to estimate dimensions of the conductive material
to be obtained. Further, since the shrinkage in volume of the conductive material
obtained is small, there is an advantage that closer adhesion thereof with the wiring
board or the lead frame can be provided.
[0076] In the method for producing the third light-emitting device, the sintering step may
be carried out in non-oxidizing atmosphere, ambient atmosphere, vacuum atmosphere,
oxygen atmosphere, mixture gas atmosphere, or airflow. The sintering step preferably
is carried out in ambient atmosphere, since this makes the formation economical.
[0077] In the method for producing the first light-emitting device and the method for producing
the second light-emitting device, the step for applying a conductive material composition
over a substrate is not limited particularly as long as the conductive material composition
can be applied over a surface of a substrate, but the step may be carried out by printing,
coating, or the like. Examples of the printing include screen printing, offset printing,
ink jet printing, flexographic printing, dispenser printing, gravure printing, stamping,
dispensing, squeeze printing, silk screen printing, spraying, and brush coating. Among
these, screen printing, stamping, or dispensing is preferable. The conductive material
composition thus applied has a thickness of, for example, 3 µm to 100 µm, preferably
3 µm to 50 µm, and more preferably 5 µm to 20 µm. For a light-emitting device having
a size of 0.5 mm square or smaller, stamping or dispensing is preferable, between
which stamping is more preferable. The stamping makes it possible to apply the composition
accurately to fine regions, and furthermore, to increase the working speed.
[0078] In the method for producing the third light-emitting device, the step for applying
a conductive paste over a substrate is not limited particularly as long as the conductive
paste can be applied over a surface of a substrate, but the step may be carried out
by printing, coating, or the like. Examples of the printing include screen printing,
offset printing, ink jet printing, flexographic printing, dispenser printing, gravure
printing, stamping, dispensing, squeeze printing, silk screen printing, spraying,
and brush coating. Among these, screen printing, stamping, or dispensing is preferable.
The conductive paste thus applied has a thickness of, for example, 3 µm to 100 µm,
preferably 3 µm to 50 µm, and more preferably 5 µm to 20 µm. For a light-emitting
device having a size of 0.5 mm square or smaller, stamping or dispensing is preferable,
between which stamping is more preferable. The stamping makes it possible to apply
the paste accurately to fine regions, and furthermore, to increase the working speed.
[0079] Each of the method for producing the first light-emitting device, the method for
producing the second light-emitting device, and the method for producing the third
light-emitting device may further include the step of laying metal wiring between
electrodes of the light-emitting element and a wiring portion of the wiring board
or the lead frame. Here, the metal wiring preferably is made of gold, silver, copper,
or aluminum, and more preferably, gold. In the case where the metal wiring is made
of gold, a stable bonding property is achieved, and corrosion less likely occurs.
[0080] Further, each of the method for producing the first light-emitting device, the method
for producing the second light-emitting device, and the method for producing the third
light-emitting device may further include the step of sealing the light-emitting device
with a resin, an air-tight cover, or a non-air-tight cover. Examples of the resin
used in the sealing step include epoxy resins, phenol resins, acrylic resins, polyimide
resins, silicone resins, urethane resins, and thermoplastic resins. Among these, silicone
resins are preferable, since a light-emitting device having excellent heat resistance
and light resistance as well as long lifetime can be produced. As a material for the
air-tight cover or the non-air-tight cover, the following can be used: inorganic glass;
polyacrylic resin; polycarbonate resin; polyolefin resin; and norbornene resin. Among
these, inorganic glass is preferable, since a light-emitting device having excellent
heat resistance and light resistance as well as long lifetime can be produced.
[0081] A light-emitting device, obtained by the method for producing a light-emitting device
according to the present invention, is configured so that the conductive material
is disposed between the wiring substrate or the lead frame, and the light-emitting
element. The conductive material has a thickness of, for example, 2 µm to 80 µm, preferably
2 µm to 40 µm, and more preferably 3 µm to 15 µm.
[0082] The method for producing a light-emitting device according to the present invention
preferably further includes the step of applying an adhesive over the conductive material.
With the step of applying the adhesive, the adhesion between the wiring board and
the conductive material can be improved. A conductive material made of the conventional
conductive composition containing an adhesive had a problem in that metal particles
were insufficiently dense and an electric resistance was high. In contrast, with the
method of the present invention, metal particles are sufficiently dense, and consequently,
a conductive material having a low electric resistance can be obtained. In the case
where such a method of the present invention further includes the step of applying
an adhesive over the conductive material, it is possible to cause the conductive material
to firmly adhere to the wiring board. As a result, a conductive material having a
low electric resistance and high adhesion to the wiring board can be obtained, which
is preferable.
[0083] Examples of the adhesive usable in the foregoing method include epoxy adhesives,
phenol adhesives, acrylic adhesives, polyimide adhesives, silicone adhesives, urethane
adhesives, and thermoplastic adhesives. Among these, epoxy adhesives are preferable
as the foregoing adhesive.
[0084] Hereinafter, the average particle diameter (median diameter) is a value determined
by the laser method, and the specific surface is a value determined by the BET method.
[Example 1]
[0085] Exothermic behaviors of mixture particles were checked by differential scanning calorimetry
(DSC) in Examples 1 to 5 and Comparative Examples 1 to 5.
Specifically, 5 mg of mixture particles were sampled, and exothermic behaviors of
the same were checked by differential scanning calorimetry (DSC). In the DSC measurement,
the temperature was increased by 10°C per minute, from room temperature to 250°C.
At 250°C, the mixture particles were placed in an anodized aluminum container, and
a lid was fitted thereafter. The atmosphere for the measurement was ambient atmosphere
or nitrogen atmosphere. In the case where the nitrogen atmosphere was used for the
measurement, the fitting of the lid was carried out in a glove box filled with nitrogen.
It should be noted that alumina particles were used as a reference material. The compositional
details of mixture particles, the atmosphere used for the measurement, the temperature
at which heat generation starts, the amount of heat generated, and the state of fusion
(fused / not fused) after measurement are shown in Table 1. In Table 1, "Silver" refers
to silver particles having an average particle diameter of 2.0 µm to 3.2 µm (produced
by Fukuda Metal Foil & Powder Co., Ltd., product name: "AgC-239"), "Silver (I) oxide"
refers to silver (I) oxide (Ag
2O) particles having an average particle diameter of 18.5 µm (produced by Wako Pure
Chemical Industries, Ltd., product name: "Silver (I) Oxide"), and "Silver (II) oxide"
refers to silver (II) oxide (AgO) particles having an average particle diameter of
10.6 µm (produced by Wako Pure Chemical Industries, Ltd., product name: "Silver (II)
Oxide").
[0086] Further, the silver particles used are as follows:
Silver particles produced by Fukuda Metal Foil & Powder Co., Ltd., having a product
name of "AgC-239", have an average particle diameter (median diameter) of 2.0 µm to
3.2 µm, and a specific surface of 0.6 to 0.9 m2/g.
Silver particles produced by Mitsui Mining & Smelting Co., Ltd., having a product
name of "FHD", have an average particle diameter (median diameter) of 0.3 µm, and
a specific surface of 2.54 m2/g.
Silver particles produced by Mitsui Mining & Smelting Co., Ltd., having a product
name of "EHD", have an average particle diameter (median diameter) of 0.5 µm, and
a specific surface of 1.70 m2/g.
Silver particles produced by Wako Pure Chemical Industries, Ltd., having a product
name of "Silver (I) Oxide", have an average particle diameter (median diameter) of
18.5 µm.
Silver particles produced by Wako Pure Chemical Industries, Ltd., having a product
name of "Silver (II) Oxide", have an average particle diameter (median diameter) of
10.6 µm.
[0087]
[Table 1]
Ex. / Comp. Ex. |
Compositional details of particles |
Atmosphere used for measurement |
Temperature of heat generation start
(°C) |
Amount of generated heat
(mJ/mg) |
State of fusion |
Silver
(wt%) |
Silver (I) Oxide
(wt%) |
Silver (II) Oxide
(wt%) |
Ex. 1 |
100 |
0 |
0 |
Ambient atmosphere |
138 |
2.85 |
Fused |
Comp. Ex. 1 |
100 |
0 |
0 |
Nitrogen Atmosphere |
130 |
0.81 |
Not fused |
Comp. Ex. 2 |
0 |
100 |
0 |
Ambient atmosphere |
98 |
6.18 |
Not fused |
Comp. Ex. 3 |
0 |
100 |
0 |
Nitrogen Atmosphere |
127 |
1.69 |
Not fused |
Ex. 2 |
90 |
10 |
0 |
Ambient atmosphere |
108 |
97 |
Fused |
Ex. 3 |
90 |
10 |
0 |
Nitrogen Atmosphere |
107 |
92.5 |
Fused |
Comp. Ex. 4 |
0 |
0 |
100 |
Ambient atmosphere |
147 |
21.8 |
Not fused |
Comp. Ex. 5 |
0 |
0 |
100 |
Nitrogen Atmosphere |
136 |
25.4 |
Not fused |
Ex. 4 |
90 |
0 |
10 |
Ambient atmosphere |
103 |
63.3 |
Fused |
Ex. 5 |
90 |
0 |
10 |
Nitrogen Atmosphere |
111 |
75.6 |
Fused |
[0088] As shown in Table 1, the results of Example 1 and Comparative Example 1 proved that
when the second conductive material composition containing silver particles having
an average particle diameter (median diameter) of 0.1 µm to 15 µm was heated in ambient
atmosphere, the particles were fused. Besides, the result that an amount of generated
heat in Example 1 was very small proved that any problem due to intense heat generation
did not occur.
[0089] As shown in Table 1, the results of Comparative Examples 2 to 5 proved that when
either only silver (I) oxide particles or only silver (II) oxide particles were heated
in nitrogen atmosphere or ambient atmosphere, the particles were not fused.
[0090] As shown in Table 1, the results of Examples 2 to 5 proved that in the case of mixture
particles containing silver particles and silver (I) oxide particles, and in the case
of mixture particles containing silver particles and silver (II) oxide particles,
an amount of generated heat was relatively large. This amount of generated heat was
several tens of times greater, in weight terms, than an amount of generated heat when
particles of silver oxide of either type alone were heated. This fact proved that
the silver particles and the silver oxide particles reacted at portions where they
were in contact with one another. Further, it was proved that even in nitrogen atmosphere
containing no oxygen, fusion occurred when mixture particles containing silver particles
and silver oxide particles were heated. In other words, it can be presumed that silver
oxide particles reacted with silver particles, thereby becoming a source of oxygen.
[Reference Example 1]
[0091] Silver particles having an average particle diameter of 10 µm (produced by Fukuda
Metal Foil & Powder Co., Ltd., product name: "AgC-224", 2.5 g), and 2-ethyl-1,3-hexanediol
(0.3 g) were mixed at 25°C, whereby a conductive paste was obtained. The conductive
paste thus obtained was applied over a glass substrate (thickness: 1 mm) by screen
printing, so as to have a thickness of 200 µm. The glass substrate over which the
conductive paste was applied was heated in nitrogen atmosphere at 150°C. The obtained
wiring had a thickness of 160 µm to 190 µm, and an electric resistance of 9.9×10
-6 Ω·cm.
[Reference Example 2]
[0092] An experiment was carried out in the same manner as that in Reference Example 1 except
that the heating temperature was set at 300°C, instead of 150°C. The obtained wiring
had an electric resistance of 4.2×10
-6 Ω·cm.
[Example 6]
[0093] Silver particles (produced by Fukuda Metal Foil & Powder Co., Ltd., product name:
"AgC-224", 1.75 g), and silver (II) oxide particles having an average particle diameter
of 10 µm (produced by Wako Pure Chemical Industries, Ltd., product name: "Silver (II)
Oxide", 1.25 g) were mixed at 25°C, whereby a first conductive material composition
was obtained. The first conductive material composition thus obtained was applied
over a glass substrate (thickness: 1 mm) by screen printing, so as to have a thickness
of 200 µm. The glass substrate over which the first conductive material composition
was applied was heated in nitrogen atmosphere of 150°C. The obtained wiring had a
thickness of 160 µm to 190 µm, and an electric resistance of 4.9×10
-5 Ω·cm.
[Example 7]
[0094] An experiment was carried out in the same manner as that in Example 6 except that,
as atmosphere used for heating, ambient atmosphere was used in place of nitrogen atmosphere.
The obtained wiring had an electric resistance of 4.4×10
-5 Ω·cm.
[Example 8]
[0095] An experiment was carried out in the same manner as that in Example 6 except that
the heating temperature was set at 300°C, instead of 150°C. The obtained wiring had
an electric resistance of 1.3×10
-5 Ω·cm.
[Example 9]
[0096] An experiment was carried out in the same manner as that in Example 7 except that
the heating temperature was set at 300°C, instead of 150°C. The obtained wiring had
an electric resistance of 1.2×10
-5 Ω·cm.
[Example 10]
[0097] An experiment was carried out in the same manner as that in Example 6 except that
silver (II) oxide particles having an average particle diameter of 0.3 µm (1.25 g)
were used in place of the silver (II) oxide particles having an average particle diameter
of 10 µm. The obtained wiring had an electric resistance of 3.9×10
-5 Ω·cm.
[Example 11]
[0098] An experiment was carried out in the same manner as that in Example 10 except that,
as atmosphere used for heating, ambient atmosphere was used in place of nitrogen atmosphere.
The obtained wiring had an electric resistance of 4.8×10
-5 Ω·cm.
[Example 12]
[0099] An experiment was carried out in the same manner as that in Example 10 except that
the heating temperature was set at 300°C, instead of 150°C. The obtained wiring had
an electric resistance of 2.2×10
-5 Ω·cm.
[Example 13]
[0100] An experiment was carried out in the same manner as that in Example 11 except that
the heating temperature was set at 300°C, instead of 150°C. The obtained wiring had
an electric resistance of 3.3·10
-5 Ω·cm.
[Reference Example 3]
[0101] An experiment was carried out in the same manner as that in Reference Example 1 except
that silver particles having an average particle diameter of 0.3 µm (produced by Mitsui
Mining & Smelting Co., Ltd., product name: "FHD", 2.5 g) were used in place of the
silver particles having an average particle diameter of 10 µm. The obtained wiring
had an electric resistance of 1.1×10
-5 Ω·cm.
[Reference Example 4]
[0102] An experiment was carried out in the same manner as that in Reference Example 2 except
that silver particles having an average particle diameter of 0.3 µm (produced by Mitsui
Mining & Smelting Co., Ltd., product name: "FHD", 2.5 g) were used in place of the
silver particles having an average particle diameter of 10 µm. The obtained wiring
had an electric resistance of 5.2×10
-5 Ω·cm.
[Example 14]
[0103] An experiment was carried out in the same manner as that in Example 6 except that
silver particles having an average particle diameter of 0.3 µm (1.75 g) were used
in place of the silver particles having an average particle diameter of 10 µm. The
obtained wiring had an electric resistance of 4.3×10
-5 Ω·cm.
[Example 15]
[0104] An experiment was carried out in the same manner as that in Example 14 except that,
as atmosphere used for heating, ambient atmosphere was used in place of nitrogen atmosphere.
The obtained wiring had an electric resistance of 4.9×10
-5 Ω·cm.
[Example 16]
[0105] An experiment was carried out in the same manner as that in Example 14 except that
the heating temperature was set at 300°C, instead of 150°C. The obtained wiring had
an electric resistance of 1.2×10
-5 Ω·cm.
[Example 17]
[0106] An experiment was carried out in the same manner as that in Example 18 except that
the heating temperature was set at 300°C, instead of 150°C. The obtained wiring had
an electric resistance of 1.2×10
-5 Ω·cm.
[Example 18]
[0107] An experiment was carried out in the same manner as that in Example 10 except that
silver (II) oxide particles having an average particle diameter of 0.3 µm (1.75 g)
were used in place of the silver (II) oxide particles having an average particle diameter
of 10 µm. The obtained wiring had an electric resistance of 4.7×10
-5 Ω·cm.
[Example 19]
[0108] An experiment was carried out in the same manner as that in Example 14 except that,
as atmosphere used for heating, ambient atmosphere was used in place of nitrogen atmosphere.
The obtained wiring had an electric resistance of 3.9×10
-5 Ω·cm.
[Example 20]
[0109] An experiment was carried out in the same manner as that in Example 18 except that
the heating temperature was set at 300°C, instead of 150°C. The obtained wiring had
an electric resistance of 2.2×10
-5 Ω·cm.
[Example 21]
[0110] An experiment was carried out in the same manner as that in Example 19 except that
the heating temperature was set at 300°C, instead of 150°C. The obtained wiring had
an electric resistance of 1.5×10
-5 Ω·cm.
[0111] The silver particles used in Reference Examples 1 to 4 and Examples 6 to 21 are as
follows:
Silver particles produced by Fukuda Metal Foil & Powder Co., Ltd., having a product
name of "AgC-224", have an average particle diameter (median diameter) of 6.5 µm to
9.0 µm, and a specific surface of 0.25 m2/g to 0.40 m2/g.
Silver particles produced by Mitsui Mining & Smelting Co., Ltd., having a product
name of "FHD", have an average particle diameter (median diameter) of 0.3 µm, and
a specific surface of 2.54 m2/g.
Silver particles produced by Wako Pure Chemical Industries, Ltd., having a product
name of "Silver (II) Oxide", have an average particle diameter (median diameter) of
10.6 µm.
Silver (II) oxide particles having an average particle diameter of 0.3 µm were produced
in-house in the following manner. Each of silver nitrate and ammonium persulfate was
dissolved in pure water, and solutions obtained were mixed and stirred; then, particles
precipitated were settled out, separated, and washed with water.
[0112] Table 2 shows the compositional details of conductive pastes in Reference Examples
1 to 4 and the compositional details of conductive material compositions in examples
6 to 21, as well as, as to each of the conductive pastes and the conductive material
compositions, the heating temperature, the atmosphere used for heating, and a resistance
of a conductive material obtained after heating. In Table 2, "Silver 10 µm" refers
to silver particles having an average particle diameter of 6.5 µm to 9.0 µm (produced
by Fukuda Metal Foil & Powder Co., Ltd., product name: AgC-224), "Silver 0.3 µm" refers
to silver particles having an average particle diameter of 0.3 µm (produced by Mitsui
Mining & Smelting Co., Ltd., product name: "FHD"), "Silver (II) oxide 10 µm" refers
to silver (II) oxide (AgO) particles having an average particle diameter of 10.6 µm
(produced by Wako Pure Chemical Industries, Ltd., product name: "Silver (II) oxide"),
and "Silver (II) oxide 0.3 µm" refers to silver (II) oxide (AgO) particles having
an average particle diameter of 0.3 µm (produced in-house).
[0113]
[Table 2]
Example |
Compositional details of particles |
Heating temp.
(°C) |
Atmosphere used for heating |
Resistance
(Ω·cm) |
Silver 10 µm
(wt%) |
Silver 0.3 µm
(wt%) |
Silver (II) oxide 10 µm
(wt%) |
Silver (II) oxide 0.3 µm
(wt%) |
Ref. Ex. 1 |
100 |
0 |
0 |
0 |
150 |
Ambient atm. |
9.9×10-6 |
Ref. Ex. 2 |
100 |
0 |
0 |
0 |
300 |
Ambient atm. |
4.2×10-6 |
Ex. 6 |
70 |
0 |
30 |
0 |
150 |
Nitrogen atm. |
4.9×10-5 |
Ex. 7 |
70 |
0 |
30 |
0 |
150 |
Ambient atm. |
4.4×10-5 |
Ex. 8 |
70 |
0 |
30 |
0 |
300 |
Nitrogen atm. |
1.3×10-5 |
Ex. 9 |
70 |
0 |
30 |
0 |
300 |
Ambient atm. |
1.2×10-5 |
Ex. 10 |
70 |
0 |
0 |
30 |
150 |
Nitrogen atm. |
3.9×10-5 |
Ex. 11 |
70 |
0 |
0 |
30 |
150 |
Ambient atm. |
4.8×10-5 |
Ex. 12 |
70 |
0 |
0 |
30 |
300 |
Nitrogen atm. |
2.2×10-5 |
Ex. 13 |
70 |
0 |
0 |
30 |
300 |
Ambient atm. |
3.3×10-5 |
Ref. Ex. 3 |
0 |
100 |
0 |
0 |
150 |
Ambient atm. |
1.1×10-5 |
Ref. Ex. 4 |
0 |
100 |
0 |
0 |
300 |
Ambient atm. |
5.2×10-5 |
Ex. 14 |
0 |
70 |
30 |
0 |
150 |
Nitrogen atm. |
4.3×10-5 |
Ex. 15 |
0 |
70 |
30 |
0 |
150 |
Ambient atm. |
4.9×10-5 |
Ex. 16 |
0 |
70 |
30 |
0 |
300 |
Nitrogen atm. |
1.2×10-5 |
Ex. 17 |
0 |
70 |
30 |
0 |
300 |
Ambient atm. |
1.2×10-5 |
Ex. 18 |
0 |
70 |
0 |
30 |
150 |
Nitrogen atm. |
4.7×10-5 |
Ex. 19 |
0 |
70 |
0 |
30 |
150 |
Ambient atm. |
3.9×10-5 |
Ex. 20 |
0 |
70 |
0 |
30 |
300 |
Nitrogen atm. |
2.2×10-5 |
Ex. 21 |
0 |
70 |
0 |
30 |
300 |
Ambient atm. |
1.5×10-5 |
[0114] The results of Reference Examples 1 and 2 and Examples 6 to 9 shown in Table 2 proved
that when a conductive paste or a conductive material composition was heated, a higher
concentration of oxygen allowed a conductive material with a lower electric resistance
to be obtained. Further, the results also show that the heating temperature of 300°C
allowed a conductive material with a lower electric resistance to be obtained, as
compared with the heating temperature of 150°C.
As shown in Table 2, the results of Reference Examples 1 to 4 and Examples 6 to 21
proved that every conductive material that was obtained by heating the conductive
paste or the conductive material composition had an electric resistance of 5.0×10
-5 Ω·cm or less. Since such a conductive composition did not contain a resin component,
a bonding material with high reliability was obtained.
[Example 22]
[0115] A dam was formed with a mask on a glass substrate (thickness: 1 mm), and the second
conductive material composition containing silver particles having an average particle
diameter of 10 µm (produced by Fukuda Metal Foil & Powder Co., Ltd., product name:
"AgC-224", 2.5 g) was filled under pressure into the dam in such a manner that the
composition had a thickness of 200 µm and the silver particles were not be plastically
deformed. The glass substrate, on which the silver particles were thus placed, was
heated at 200°C in ambient atmosphere. The wiring obtained had a voidage of 8.2 %,
and an electric resistance of 3.7×10
-6 Ω·cm.
[Reference Example 5]
[0116] Silver particles having an average particle diameter of 10 µm (Fukuda Metal Foil
& Powder Co., Ltd., product name: "AgC-224", 2.5 g) and 2-ethyl-1,3-hexanediol (0.28
g) were mixed at 25°C, whereby a conductive paste was obtained. The content of 2-ethyl-1,3-hexanediol
in the paste was 10 wt%. The conductive paste obtained was applied over a glass substrate
(thickness: 1 mm) by screen printing, so as to have a thickness of 200 µm. The glass
substrate, over which the conductive paste was applied, was heated at 200°C in ambient
atmosphere. The wiring obtained had a voidage of 21.3 %, and an electric resistance
of 8.3×10
-6 Ω·cm.
[Reference Example 6]
[0117] An experiment was carried out in the same manner as that in Reference Example 5 except
that the weight of 2-ethyl-1,3-hexanediol was set at, not 0.28 g, but 0.44 g, and
the content thereof in the paste was set at 15 wt%. The wiring obtained had a voidage
of 27.5 %, and an electric resistance of 1.2×10
-5 Ω·cm.
[Reference Example 7]
[0118] An experiment was carried out in the same manner as that in Reference Example 5 except
that the weight of 2-ethyl-1,3-hexanediol was set at, not 0.28 g, but 0.63 g, and
the content thereof in the paste was set at 20 wt%. The wiring obtained had a voidage
of 35.1 %, and an electric resistance of 7.2×10
-5 Ω·cm.
[Reference Example 8]
[0119] An experiment was carried out in the same manner as that in Reference Example 5 except
that the weight of 2-ethyl-1,3-hexanediol was set at, not 0.28 g, but 0.84 g, and
the content thereof in the paste was set at 30 wt%. The wiring obtained had a voidage
of 42.9 %, and an electric resistance of 3.1×10
-4 Ω·cm.
[0120] Table 3 shows the compositional details of the conductive material composition of
Example 22, and the added amount of a solvent, the voidage and resistance of a conductive
material obtained by heating the conductive paste or the conductive material composition
as to each of Reference Examples 5 to 8 An electron micrograph of the conductive material
obtained in Example 22 is shown in FIG. 1. An electron micrograph of the conductive
material obtained in Reference Example 8 is shown in FIG. 2.
[0121]
[Table 3]
Example |
Added amount of solvent
(wt%) |
Voidage
(% by area) |
Resistance
(Ω·cm) |
Ex. 22 |
0 |
8.2 |
3.7×10-6 Ω·cm |
Ref. Ex. 5 |
10 |
21.3 |
8.3×10-6 Ω·cm |
Ref. Ex. 6 |
15 |
27.5 |
1.2×10-5 Ω·cm |
Ref. Ex. 7 |
20 |
35.1 |
7.2×10-5 Ω·cm |
Ref. Ex. 8 |
30 |
42.9 |
3.1×10-4 Ω·cm |
[0122] As shown in Table 3, the results of Example 22 and Reference Examples 5 to 8 proved
that the voidage was influenced most by the amount of solvent in the conductive paste.
Further, as shown in FIG. 1, it was proved that when no solvent was used and silver
particles were filled under pressure, voids decreased, since no volume portion was
occupied by a solvent and no path for allowing volatile solvent to pass through was
needed. As shown in FIG. 2, it was proved that when a large amount of solvent was
used, the voidage increased, since certain volume portions were occupied by the solvent
and paths for discharge of vaporized solvent were needed.
[Comparative Example 6]
[0123] Silver particles (produced by Fukuda Metal Foil & Powder Co., Ltd., product name:
"AgC-239", 2.5 g), and 2-ethyl-1,3-hexanediol (0.3 g) were mixed at 25°C, whereby
a composition was obtained. The composition obtained was applied on a silver-plated
surface of an alumina substrate by stamping, and a sapphire dice having one surface
metallized with silver, in a size of 500 µm × 500 µm × 100 µm (thickness), was mounted
thereon. This was heated at 200°C in nitrogen atmosphere. A shearing power was applied
in such a direction that the dice was separated from the alumina substrate, and a
strength when the dice separated therefrom was measured. The strength was 52 gf.
[Example 23]
[0124] Silver particles (produced by Fukuda Metal Foil & Powder Co., Ltd., product name:
"AgC-239", 2.375 g), silver (II) oxide (produced by Wako Pure Chemical Industries,
Ltd., product name: "Silver (II) Oxide", 0.125 g), and 2-ethyl-1,3-hexanediol (0.3
g) were mixed at 25°C, whereby a first conductive material composition was obtained.
The composition obtained was applied on a silver-plated surface of an alumina substrate
by stamping, and a sapphire dice having one surface metallized with silver, in a size
of 500 µm × 500 µm × 100 µm (thickness), was mounted thereon. This was heated at 200°C
in nitrogen atmosphere. A shearing power was applied in such a direction that the
dice was separated from the alumina substrate, and a strength when the dice separated
therefrom was measured. The strength was 392 gf.
[Example 24]
[0125] An experiment was carried out in the same manner as that in Example 23 except that
silver particles (produced by Fukuda Metal Foil & Powder Co., Ltd., product name:
"AgC-239", 2.25 g) and silver (II) oxide (produced by Wako Pure Chemical Industries,
Ltd., product name: "Silver (II) Oxide", 0.25 g) were used in place of the silver
particles (produced by Fukuda Metal Foil & Powder Co., Ltd., product name: "AgC-239",
2.375 g) and the silver (II) oxide (produced by Wako Pure Chemical Industries, Ltd.,
product name: "Silver (II) Oxide", 0.125 g). The shear strength measured was 553 gf.
[Example 25]
[0126] An experiment was carried out in the same manner as that in Example 23 except that
silver particles (produced by Fukuda Metal Foil & Powder Co., Ltd., product name:
"AgC-239", 2.0 g) and silver (II) oxide (produced by Wako Pure Chemical Industries,
Ltd., product name: "Silver (II) Oxide", 0.5 g) were used in place of the silver particles
(produced by Fukuda Metal Foil & Powder Co., Ltd., product name: "AgC-239", 2.375
g) and the silver (II) oxide (produced by Wako Pure Chemical Industries, Ltd., product
name: "Silver (II) Oxide", 0.125 g). The shear strength measured was 478 gf.
[Example 26]
[0127] An experiment was carried out in the same manner as that in Example 23 except that
silver particles (produced by Fukuda Metal Foil & Powder Co., Ltd., product name:
"AgC-239", 1.75 g) and silver (II) oxide (produced by Wako Pure Chemical Industries,
Ltd., product name: "Silver (II) Oxide", 0.75 g) were used in place of the silver
particles (produced by Fukuda Metal Foil & Powder Co., Ltd., product name: "AgC-239",
2.375 g) and the silver (II) oxide (produced by Wako Pure Chemical Industries, Ltd.,
product name: "Silver (II) Oxide", 0.125 g). The shear strength measured was 322 gf.
[Example 27]
[0128] An experiment was carried out in the same manner as that in Example 23 except that
silver particles (produced by Fukuda Metal Foil & Powder Co., Ltd., product name:
"AgC-239", 1.25 g) and silver (II) oxide (produced by Wako Pure Chemical Industries,
Ltd., product name: "Silver (II) Oxide", 1.25 g) were used in place of the silver
particles (produced by Fukuda Metal Foil & Powder Co., Ltd., product name: "AgC-239",
2.375 g) and the silver (II) oxide (produced by Wako Pure Chemical Industries, Ltd.,
product name: "Silver (II) Oxide", 0.125 g). The shear strength measured was 157 gf.
[Example 28]
[0129] Silver particles (produced by Fukuda Metal Foil & Powder Co., Ltd., product name:
"AgC-239", 2.5 g), and 2-ethyl-1,3-hexanediol (0.3 g) were mixed at 25°C, whereby
a first conductive material composition was obtained. The composition obtained was
applied on a silver-plated surface of an alumina substrate by stamping, and a sapphire
dice having one surface metallized with silver, in a size of 500 µm × 500 µm × 100
µm (thickness), was mounted thereon. This was heated at 200°C in atmospheric nitrogen
atmosphere. A shearing power was applied in such a direction that the dice was separated
from the alumina substrate, and a strength when the dice separated therefrom was measured.
The strength was 722 gf.
[Example 29]
[0130] An experiment was carried out in the same manner as that in Example 23 except that,
as atmosphere used for heating, ambient atmosphere was used in place of nitrogen atmosphere.
The shearing strength measured was 703 gf.
[Example 30]
[0131] An experiment was carried out in the same manner as that in Example 24 except that,
as atmosphere used for heating, ambient atmosphere was used in place of nitrogen atmosphere.
The shearing strength measured was 664 gf.
[Example 31]
[0132] An experiment was carried out in the same manner as that in Example 25 except that,
as atmosphere used for heating, ambient atmosphere was used in place of nitrogen atmosphere.
The shearing strength measured was 544 gf.
[Example 32]
[0133] An experiment was carried out in the same manner as that in Example 26 except that,
as atmosphere used for heating, ambient atmosphere was used in place of nitrogen atmosphere.
The shearing strength measured was 391 gf.
[Example 33]
[0134] An experiment was carried out in the same manner as that in Example 27 except that,
as atmosphere used for heating, ambient atmosphere was used in place of nitrogen atmosphere.
The shearing strength measured was 123 gf.
[0135] As to each of Comparative Example 6 and Examples 23 to 33, Table 4 shows the content
of silver (II) oxide in a conductive material composition, the atmosphere used for
heating, and the shearing strength of a conductive material obtained.
[0136]
[Table 4]
Example |
Silver (II) oxide
(wt%) |
Atmosphere used for heating |
Shearing strength
(gf) |
Comp. Ex. 6 |
0 |
Nitrogen atm. |
52 |
Ex. 23 |
5 |
Nitrogen atm. |
392 |
Ex. 24 |
10 |
Nitrogen atm. |
553 |
Ex. 25 |
20 |
Nitrogen atm. |
478 |
Ex. 26 |
30 |
Nitrogen atm. |
322 |
Ex. 27 |
50 |
Nitrogen atm. |
157 |
Ex. 28 |
0 |
Ambient atm. |
722 |
Ex. 29 |
5 |
Ambient atm. |
703 |
Ex. 30 |
10 |
Ambient atm. |
664 |
Ex. 31 |
20 |
Ambient atm. |
544 |
Ex. 32 |
30 |
Ambient atm. |
391 |
Ex. 33 |
50 |
Ambient atm. |
123 |
[0137] As shown in Table 4, the results of Comparative Example 6 and Examples 23 to 27 proved
that when a first conductive material composition containing silver particles having
an average particle diameter of 0.1 µm to 15 µm and a metal oxide were heated, a conductive
material having a sufficient shear strength was obtained. Further, the results of
Examples 28 to 33 proved that when a first conductive material composition containing
silver particles having an average particle diameter of 0.1 µm to 15 µm was sintered
in ambient atmosphere, a conductive material having a sufficient shear strength was
obtained.
[Example 34]
[0138] Silver particles (produced by Fukuda Metal Foil & Powder Co., product name: "AgC-239",
2.5 g) and 2-ethyl-1,3-hexanediol having a boiling point of 243°C (0.44 g) were mixed
at 25°C, whereby a second conductive material composition was obtained. This composition
was applied by stamping over an aluminum oxide substrate for a light-emitting device,
with a pattern being formed on the substrate byAg/Ni plating. The area subjected to
application was a perfect circle in shape, and had a diameter of about 700 µm in size.
The application was carried out continuously 312 times, and diameters of applied areas
obtained at the first ten times immediately after the start, and those at the last
ten times in chronological order, were measured. Then, it was determined by Student's
t-test whether there was a significant difference therebetween. FIG. 3 shows a variation
of the amount of the composition applied by stamping.
[0139] As shown in FIG. 3, the results of Example 34 proved that in the case where a second
conductive material composition containing silver particles having an average particle
diameter of 0.1 µm to 10 µm and alcohol was applied by stamping, a confidence interval
with 95 % reliability with respect to the diameter average of the applied areas obtained
at the first ten times immediately after the start, and that of the applied areas
obtained at the last ten times, were substantially identical, and no significant difference
was seen therebetween. In other words, it was proved that the stamping can be carried
out using a conductive material composition containing no adhesive. Further, it was
proved that since an organic solvent having a high boiling point was contained, the
deterioration of the stamping stability due to volatilization of an organic solvent
was avoided.
[Example 35]
[0140] A 500 µm-square light-emitting element was mounted on the surface on which the conductive
material composition was applied by stamping in Example 34. Metal films were formed
by vapor deposition on a surface where the light-emitting element and the conductive
material composition were in contact with each other, and the topmost film was made
of silver (thickness: 0.2 µm). The substrate on which the light-emitting element was
mounted with the conductive material composition being interposed therebetween was
heated at 200°C for one hour in ambient atmosphere. Thereafter the substrate was cooled.
The light-emitting element exhibited a sufficient strength of bonding with the substrate.
Further, the bonded portion at which the light-emitting element and the substrate
were bonded was checked by visual observation, and the fusion of particles in the
bonding material was observed. As to the substrate on which the light-emitting element
was bonded, a die-shear strength was measured at room temperature, and was determined
to be about 0.7 kgf.
[0141] On the light-emitting element of the substrate, another aluminum oxide substrate
for a light-emitting device was mounted, and was heated further at 250°C for two hours.
Here, it was noted that the bonded portions of silver between the light-emitting element
and the substrate did not have any discoloration. As to this bonding between the light-emitting
element and the substrate, a die-shear strength was measured at room temperature,
and was determined to be about 0.7 kgf.
[0142] Next, electrodes of the light-emitting element and electrodes of the substrate were
connected with gold wiring, and were sealed with a silicone resin. In this state,
power on tests (test conditions: 25°C, 50 mA) were carried out after a lapse of 500
hours, after a lapse of 1000 hours, and after a lapse of 2000 hours. The output results
with respect to the initial outputs are shown in Table 5. It should be noted that
after a lapse of 2000 hours, no discoloration occurred at the bonded portions of silver
between the light-emitting element and the substrate.
[Comparative Example 7]
[0143] An insulative epoxy resin (curing conditions: 180°C, 2 hours) was applied by stamping
over an aluminum oxide substrate for a light-emitting device, with a pattern being
formed on the substrate by Ag/Ni plating. The applied area was a perfect circle in
shape, and had a diameter of about 700 µm in size. A light-emitting element was mounted
on the foregoing adhesive. The substrate on which the light-emitting element was thus
mounted with the adhesive provided therebetween was heated at 200°C for 1 hour in
ambient atmosphere. Thereafter, the substrate was cooled. As to the substrate on which
the light-emitting element was bonded, a die-shear strength was measured at room temperature,
and was determined to be about 1 kgf.
[0144] On the light-emitting element of the substrate, another aluminum oxide substrate
for a light-emitting device was mounted, and was heated further at 250°C for two hours.
Here, it was noted that the bonded portions of silver between the light-emitting element
and the substrate had discoloration into blackish-brownish color. As to this bonding
between the light-emitting element and the substrate, a die-shear strength was measured
at room temperature, and was determined to be about 0.4 kgf.
[0145] Next, electrodes of the light-emitting element and electrodes of the substrate were
connected with gold wiring, and were sealed with a silicone resin. In this state,
power-on tests (test conditions: 25°C, 50 mA) were carried out after a lapse of 500
hours, after a lapse of 1000 hours, and after a lapse of 2000 hours. The output results
with respect to the initial outputs are shown in Table 5. It should be noted that
after a lapse of 2000 hours, discoloration to blackish-brownish color occurred at
the bonded portions of silver between the light-emitting element and the substrate.
[Comparative Example 8]
[0146] A silver paste containing 80 wt% of a flake-form silver filler and 20 wt% of an epoxy
resin (curing conditions: 200°C, 1.5 hours) was applied by stamping over an aluminum
oxide substrate for a light-emitting device, with a pattern being formed on the substrate
byAg/Ni plating. The applied area was a perfect circle in shape, and had a diameter
of about 700 µm in size. A light-emitting element was mounted on the foregoing adhesive.
The substrate on which the light-emitting element was thus mounted with the adhesive
provided therebetween was heated at 200°C for 1 hour in ambient atmosphere. Thereafter,
the substrate was cooled. As to the substrate on which the light-emitting element
was bonded, a die-shear strength was measured at room temperature, and was determined
to be about 0.7 kgf.
[0147] On the light-emitting element of the substrate, another aluminum oxide substrate
for a light-emitting device was mounted, and was heated further at 250°C for two hours.
Here, it was noted that the bonded portions of silver between the light-emitting element
and the substrate had discoloration into blackish-brownish color. As to this bonding
between the light-emitting element and the substrate, a die-shear strength was measured
at room temperature, and was determined to be about 0.6 kgf.
[0148] Next, electrodes of the light-emitting element and electrodes of the substrate were
connected with gold wiring, and were sealed with a silicone resin. In this state,
power-on tests (test conditions: 25°C, 50 mA) were carried out after a lapse of 500
hours, after a lapse of 1000 hours, and after a lapse of 2000 hours. The output results
with respect to the initial outputs are shown in Table 5. It should be noted after
a lapse of 2000 hours, discoloration to blackish-brownish color occurred at the bonded
portions of silver between the light-emitting element and the substrate.
[0149]
[Table 5]
|
Bonding |
After lapse of 500 hours |
After lapse of 1000 hours |
After lapse of 2000 hours |
Ex. 35 |
Bonding by Ag fusion |
98 % |
98% |
97 % |
Comp. Ex. 7 |
Bonding with insulative epoxy resin |
95 % |
87 % |
73 % |
Comp. Ex. 8 |
Bonding with epoxy resin containing flake-form silver filler |
93 % |
82% |
64 % |
[0150] Table 5 shows that in the case of the bonding obtained in Example 35, the output
only slightly decreased even after a lapse of 2000 hours. On the other hand, it is
shown that in the cases of the bonding obtained in Comparative Example 7 and that
in Comparative Example 8, the outputs significantly decreased after a lapse of 2000
hours.
[Example 36]
[0151] To silver particles (produced by Fukuda Metal Foil & Powder Co., Ltd., product name:
"AgC-239", 2.5 g), silver oxide having an average particle diameter of 0.5 µm to 1.0
µm (principal component: AgO) was added at a ratio by weight of 10 wt%, and tripropylene
glycol monomethyl ether was added thereto so that a ratio by weight of the same to
a solid portion was 85:15, and these were mixed at 25°C, whereby a first conductive
material composition was prepared. At a position of a lead frame where a light-emitting
element was mounted, which was obtained by insert molding of a resin portion that
would become a reflector, the conductive material composition was applied by stamping.
It should be noted that a surface at the position of the lead frame where a light-emitting
element was mounted was coated further with silver (thickness: 2 µm) by vapor deposition.
On the conductive material composition thus coated with silver, a light-emitting element
having a size of 300 µm square was disposed. The lead frame on which the light-emitting
element was disposed was heated at 180°C for two hours in non-oxidizing atmosphere,
taken out of the atmosphere, and cooled. The bonding between the light-emitting element
and the substrate provided a sufficient strength. The bonded portion at which the
light-emitting element and the substrate were bonded was checked by visual observation,
and the fusion of particles in the bonding material was observed. Further, it was
noted that neither degradation nor discoloration occurred to the lead frame resin
portion since the heating was performed in non-oxidizing atmosphere. As to the substrate
on which the light-emitting element was bonded, a die-shear strength was measured
at room temperature, and was determined to be about 0.3 kgf.
[0152] On the light-emitting element of the substrate, another aluminum oxide substrate
for a light-emitting device was mounted, and was heated further at 250°C for two hours.
Here, it was noted that the bonded portions of silver between the light-emitting element
and the substrate had no discoloration. As to this bonding between the light-emitting
element and the substrate, a die-shear strength was measured at room temperature,
and was determined to be about 0.3 kgf.
[0153] Next, electrodes of the light-emitting element and electrodes of the substrate were
connected with gold wiring, and were sealed with a silicone resin. In this state,
power-on tests (test conditions: 25°C, 50 mA) were carried out after a lapse of 500
hours, after a lapse of 1000 hours, and after a lapse of 2000 hours. The output results
with respect to the initial outputs are shown in Table 6. It should be noted that
after a lapse of 2000 hours, no discoloration occurred at the bonded portions of silver
between the light-emitting element and the substrate.
[Comparative Example 9]
[0154] An experiment was carried out in the same manner as that in Example 36 except that
an epoxy resin (curing conditions: 180°C, 2 hours) was used in place of the first
conductive material composition. As to a substrate on which a light-emitting element
was bonded, a die-shear strength was measured at room temperature, and was determined
to be about 0.4 kgf.
[0155] On the light-emitting element of the substrate, another aluminum oxide substrate
for a light-emitting device was mounted, and was heated further at 250°C for two hours.
Here, it was noted that the bonded portions of silver between the light-emitting element
and the substrate had discoloration into blackish-brownish color. As to this bonding
between the light-emitting element and the substrate, a die-shear strength was measured
at room temperature, and was determined to be about 0.1 kgf.
[0156] Next, electrodes of the light-emitting element and electrodes of the substrate were
connected with gold wiring, and were sealed with a silicone resin. In this state,
power-on tests (test conditions: 25°C, 50 mA) were carried out after a lapse of 500
hours, after a lapse of 1000 hours, and after a lapse of 2000 hours. The output results
with respect to the initial outputs are shown in Table 6. It should be noted that
after a lapse of 2000 hours, discoloration to blackish-brownish color occurred at
the bonded portions of silver between the light-emitting element and the substrate.
[Comparative Example 10]
[0157] An experiment was carried out in the same manner as that in Example 36 except that
anAg paste (curing conditions: 200°C, 1.5 hours) containing 80 wt% of a silver filler
and 20 wt% of an epoxy resin was used in place of the first conductive material composition.
As to a substrate on which a light-emitting element was bonded, a die-shear strength
was measured at room temperature, and was determined to be about 0.3 kgf.
[0158] On the light-emitting element of the substrate, another aluminum oxide substrate
for a light-emitting device was mounted, and was heated further at 250°C for two hours.
Here, it was noted that the bonded portions of silver between the light-emitting element
and the substrate had discoloration into blackish-brownish color. As to this bonding
between the light-emitting element and the substrate, a die-shear strength was measured
at room temperature, and was determined to be about 0.1 kgf.
[0159] Next, electrodes of the light-emitting element and electrodes of the substrate were
connected with gold wiring, and were sealed with a silicone resin. In this state,
power-on tests (test conditions: 25°C, 50 mA) were carried out after a lapse of 500
hours, after a lapse of 1000 hours, and after a lapse of 2000 hours. The output results
with respect to the initial outputs are shown in Table 6. It should be noted after
a lapse of 2000 hours, discoloration to blackish-brownish color occurred at the bonded
portions of silver between the light-emitting element and the substrate.
[0160]
[Table 6]
|
Bonding |
After lapse of 500 hours |
After lapse of 1000 hours |
After lapse of 2000 hours |
Ex. 36 |
Bonding by Ag fusion |
96% |
95% |
95% |
Comp. Ex. 9 |
Bonding with insulative epoxy resin |
90% |
83% |
70% |
Comp. Ex. 10 |
Bonding with epoxy resin containing flake-form silver filler |
88% |
79% |
65 % |
[0161] As shown in Table 6, it is noted that in the case of the bonding obtained in Example
36, the output only slightly decreased even after a lapse of 2000 hours. On the other
hand, it was noted that in the cases of the bonding obtained in Comparative Example
9 and that in Comparative Example 10, the outputs significantly decreased after a
lapse of 2000 hours.
Industrial Applicability
[0162] The method for producing a conductive material according to present invention can
be used for the purpose of producing heat-resistant power wiring, component electrodes,
die attaches, microbumps, flat panels, solar wiring, and the like, the purpose of
wafer bonding, and the purpose of producing electronic components produced with use
of these in combination. The method for producing a conductive material according
to the present invention also can be used for, for example, producing a light-emitting
device in which a light-emitting element such as LED or LD is used.